German patent No. 27 16 471 discloses a brake system of this type wherein a compressed air pump can be connected to a high pressure chamber of a brake power booster by way of an electrically operable solenoid valve. The pressure in the high pressure chamber is adjusted by way of a pulsed electric actuation of the solenoid valve. A low pressure chamber is directly connected to a vacuum pump.
A disadvantage of this known brake system is the use of a solenoid valve which is complicated and costly and requires an electric or electronic controlling or regulating unit for the actuation. The compressed air pump as well as the vacuum pump are pumps with uninterrupted operation which permanently develop the maximum possible excess pressure or vacuum. The result is a high energy consumption because the full pump rate must be provided in each operating condition of the brake system.
Therefore, an object of the present invention is to overcome the above-mentioned shortcomings, i.e., to suggest an inexpensive, energy-saving and simple generic brake system.